Reverse engineering or digitizing a physical part is a critical task for any mold and pattern shop. Most customers say that they design all of their parts on a CAD system;

however, the reality isn’t that simple. Many older parts were designed on a drafting board before the company started heavily using CAD and others were done on an older CAD system whose files haven’t been converted over to their new system. In many other cases, the parts, molds or patterns were originally designed on a ,CAD system but changes were made by hand to the mold or pattern after the design was completed and the CAD file was never updated. Whatever the reason, nearly every mold shop is continually asked to duplicate or RE parts.

Many moldmakers use CMMs or CNC (computerized numerical control) milling machine tools for RE. The problem with this approach is the amount of time required. It might take about 30 minutes to set up the machine and from that point on it works without a lot of attention.

But parts have become so complex today that it takes at least tens of thousands or sometimes even hundreds of thousands of points to create an accurate 3-D model. Getting this many points takes hours, or even days, on a typical machining center or CMM. The contact digitizer probes used on these machines also are limited in the geometries that they can accurately reverse engineer.

Some parts have undercuts or indentations that are too small for the probe to enter. There also are some parts with 3-D contours that are so complicated that it would just take too long to accurately digitize them with point-by-point. The resulting coordinate points also have an offset calculation that is needed to vectorize the data that rarely gets calculated into the measurement accurately due to the constantly changing vector representing where on the touch probe sphere, that contact with the part was made.

Another critical measurement task for nearly every moldmaker is the need to provide accurate measurement of prototype parts in order to evaluate the performance of the mold and process. Once the engineers are satisfied, they set up the production operation and produce the first article parts. These parts are carefully measured and compared to the manufacturer’s specifications. The problem with using a CMM for these measurements is that as the geometrical complexity grows, the number of points required for accurate measurements increases at an exponential rate.

This greatly increases the amount of time needed to capture points one at a time on a CMM. Small high detail parts can be extremely difficult to measure without deflecting the part when touching it with a mechanical touch probe. For example, delicate, plastic parts like those of cell phones easily deflect due to very thin walls and difficult to probe fine detail geometry.